We are studying chemotaxis, the directed migration of cells along a chemical gradient. Our attention has been centered on this response in connective tissue cells (fibroblasts) and phagocytes. Cultured human breast carcinoma cells from fibrotic tumors have been shown to produce a potent protein attractant (Mr=100,000 for fibroblasts. More attractant is produced by tumor cells that are enclosed in fibrous capsules than by tumor cells which are not. The attractant, when instilled into slow releasing devices in vivo in mice, stimulated in situ a fibrotic mass. The implication of this work is that the formation of the fibrotic capsule surrounding certain breast carcinomas is induced principally by cells brought to the tumor by attractants released by the tumor cells. Tumors also produce immunosuppressive effects in the host, some of which are directed against phagocytes. A low molecular weight (Mr = 500) material, partially purified by chromatography, inhibits the chemotactic responses and the production of active oxygen in both monocytes and neutrophils. The material is heterogeneous and has properties of a glycolipid. Synthetic peptides containing sequences identical to products of virally transformed cells have also been found to inhibit chemotaxis. They appear to act by affecting phospholipase, a membrane enzyme crucial to chemotaxis. These findings suggest that tumors have a variety of defenses against the host's immune system. On the basis of these studies it may be possible to design highly effective anti-inflammatory agents and to learn more about oral inflammatory diseases as well as cancer.